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AgBiSe2 undergoes two structural transitions in its service temperature range. Increasing entropy by alloying is considered an effective solution for modulating phase transition, but the efficacy of increasing entropy is limited by solubility and the selection of alloying components depends on trial and error. This study first confirmes that trigonal AgBiSe2 is metavalently bonded and searches metavalent PbTe as the alloying material based on the 2D map spanned by quantitative chemical bonding descriptors of electrons transferred (ET) and electrons shared (ES). The large solubility can be explained by the same bonding mechanism. PbTe alloying successfully stabilizes cubic AgBiSe2 to room temperature. Further, by optimizing the carrier concentration, the average ZT value from 300 to 773 K of (AgBiSe2)0.7(PbTe)0.3Cu0.02 reaches 0.42, which is 40% higher than that of pristine AgBiSe2. Simultaneously, heavy alloying leads to solid solution strengthening with enhanced hardness. This study not only paves the way for practical applications of AgBiSe2‐based materials but also provides an effective strategy for screening potential alloying candidates to solve the structure‐transition issue from the viewpoint of chemical bonding. [ABSTRACT FROM AUTHOR]

Thermoelectric refrigeration is one of the mature techniques used for cooling applications, with the great advantage of miniaturization over traditional compression refrigeration. Due to the anisotropic thermoelectric properties of n‐type bismuth telluride (Bi2Te3) alloys, these two common methods, including the liquid phase hot deformation (LPHD) and traditional hot forging (HF) methods, are of considerable importance for texture engineering to enhance performance. However, their effects on thermoelectric and mechanical properties are still controversial and not clear yet. Moreover, there has been little documentation of mechanical properties related to micro‐refrigeration applications. In this work, the above‐mentioned methods are separately employed to control the macroscopic grain orientation for bulk n‐type Bi2Te3 samples. The HF method enabled the stabilization of both composition and carrier concentration, therefore yielding a higher quality factor to compare with that of LPHD samples, supported by DFT calculations. In addition to superior thermoelectric performance, the HF sample also exhibited robust mechanical properties due to the presence of nano‐scale distortion and dense dislocation, which is the prerequisite for realizing ultra‐precision machining. This work helps to pave the way for the utilization of n‐type Bi2Te3 for commercial micro‐refrigeration applications. [ABSTRACT FROM AUTHOR]

The hexagonal Bi0.33(Bi6S9)Br intermediate was incorporated to enhance the thermoelectric properties of Bi2S3 by a facile synthesis process. As a result of the increase of carrier concentration caused by Br diffusion doping and the enhancement of phonon scattering caused by pores, point defects, and secondary phase interfaces, a maximum ZT value of 0.64 was achieved at 773 K in Bi2S3 + 5% Bi0.33(Bi6S9)Br. This study provides a strategy for achieving Br doping in the Bi2S3 system by adding the Bi0.33(Bi6S9)Br intermediate alloy, while the nanostructure was maintained in the matrix, which may be also suitable for other thermoelectric materials to obtain higher performance. [ABSTRACT FROM AUTHOR]

The recent growing energy crisis draws considerable attention to high‐performance thermoelectric materials. n‐type bismuth telluride is still irreplaceable at near room temperature for commercial application, and therefore, is worthy of further investigation. In this work, nanostructured Bi2Te3 polycrystalline materials with highly enhanced thermoelectric properties are obtained by alkali metal Na solid solution. Na is chosen as the cation site dopant for n‐type polycrystalline Bi2Te3. Na enters the Bi site, introducing holes in the Bi2Te3 matrix and rendering the electrical conductivity tunable from 300 to 1800 Scm–1. The solid solution limit of Na in Bi2Te3 exceeds 0.3 wt%. Owing to the effective solid solution, the Fermi level of Bi2Te3 is properly regulated, leading to an improved Seebeck coefficient. In addition, the scattering of both charge carriers and phonons is modulated, which ensured a high‐power factor and low lattice thermal conductivity. Benefitting from the synergistic optimization of both electrical and thermal transport properties, a maximum figure of merit (ZT) of 1.03 is achieved at 303 K when the doping content is 0.25 wt%, which is 70% higher than that of the pristine sample. This work disclosed an effective strategy for enhancing the performance of n‐type bismuth telluride‐based alloy materials. [ABSTRACT FROM AUTHOR]

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Bi2S3‐based thermoelectric materials without toxic and expensive elements have a high Seebeck coefficient and intrinsic low thermal conductivity. However, Bi2S3 suffers from low electrical conductivity, which makes it a less‐than‐perfect thermoelectric material. In this work, halogen elements F, Cl, and Br from halogen acid are successfully introduced into the Bi2S3 lattice using a hydrothermal procedure to efficiently improve the carrier concentration. Compared with the pure sample, the electron concentration of the Bi2S3 sample treated with HCl is increased by two orders of magnitude. An optimal power factor of 470 µW m−1 K−2 for the Bi2S2.96Cl0.04 sample at 673 K is obtained. Density functional theory calculations reveal that an effective delocalized electron conductive network forms after Cl doping, which raises the Fermi level into the conduction bands, thus generating more free electrons and improving the conductivity of the Bi2S3‐based materials. Ultimately, an excellent ZT of ≈0.8 is achieved at 673 K for the Bi2S2.96Cl0.04 sample, which is one of the highest values reported for a state‐of‐the‐art Bi2S3 system. The energy conversion efficiency of the module reaches 2.3% at 673 K with a temperature difference of 373 K. This study offers a new method for enhancing the thermoelectric properties of Bi2S3 by adding halogen acid in the hydrothermal process for powder synthesis. [ABSTRACT FROM AUTHOR]

A Bi2Te3/Bi2S3@Bi nanocomposite with a network microstructure was successfully synthesized via a hydrothermal method and spark plasma sintering. This composite was constructed from Bi2Te3 nanoparticles and Bi2S3@Bi nanowires, and its network structure is beneficial for obtaining excellent thermoelectric performance. A ZT peak of 1.2 at 450 K was realized for the nanocomposite sample. [ABSTRACT FROM AUTHOR]

The recent growing energy crisis draws considerable attention to high‐performance thermoelectric materials. n‐type bismuth telluride is still irreplaceable at near room temperature for commercial application, and therefore, is worthy of further investigation. In this work, nanostructured Bi2Te3 polycrystalline materials with highly enhanced thermoelectric properties are obtained by alkali metal Na solid solution. Na is chosen as the cation site dopant for n‐type polycrystalline Bi2Te3. Na enters the Bi site, introducing holes in the Bi2Te3 matrix and rendering the electrical conductivity tunable from 300 to 1800 Scm–1. The solid solution limit of Na in Bi2Te3 exceeds 0.3 wt%. Owing to the effective solid solution, the Fermi level of Bi2Te3 is properly regulated, leading to an improved Seebeck coefficient. In addition, the scattering of both charge carriers and phonons is modulated, which ensured a high‐power factor and low lattice thermal conductivity. Benefitting from the synergistic optimization of both electrical and thermal transport properties, a maximum figure of merit (ZT) of 1.03 is achieved at 303 K when the doping content is 0.25 wt%, which is 70% higher than that of the pristine sample. This work disclosed an effective strategy for enhancing the performance of n‐type bismuth telluride‐based alloy materials. [ABSTRACT FROM AUTHOR]

SnSe materials have attracted extensive attention in thermoelectrics due to their low thermal conductivity. Nevertheless, the thermoelectric properties of n-type polycrystalline SnSe are still low, and metallic Sn distributed in the SnSe 1- x materials would affect the repeatability of thermoelectric performance. Herein, the thermoelectric properties of n-type polycrystalline SnSe 0.95 -based composites are highly enhanced by heterogeneous Cu doping. The carrier concentration of the SnSe 0.95 material was optimized by SnCl 2 doping. The strategy of heterogeneous Cu doping is employed in further improving the thermoelectric performance of the SnCl 2 -doped SnSe 0.95 materials. In addition, partial Cu + doping tunes the electron concentration to enhance the Seebeck coefficient. Moreover, metallic Sn distributed along the grain boundaries can be stabilized by forming Cu 6 Sn 5 alloys, which improve the thermal stability of bulk composites. Excessive Cu particles and SnCl 2 precipitates strengthen phonon scattering for lowering the lattice thermal conductivity. Ultimately, a peak ZT of 1.55 is yielded at 773 K in the SnSe 0.95 -1 wt % SnCl 2 -1 wt % Cu bulk composite, whose mechanical hardness is also increased. Hence, these results promote a feasible approach to simultaneously enhance the thermoelectric and mechanical properties of n-type SnSe-based composites, which might be worth exploring in other thermoelectric materials.

Thermoelectric refrigeration is one of the mature techniques used for cooling applications, with the great advantage of miniaturization over traditional compression refrigeration. Due to the anisotropic thermoelectric properties of n-type bismuth telluride (Bi 2 Te 3 ) alloys, these two common methods, including the liquid phase hot deformation (LPHD) and traditional hot forging (HF) methods, are of considerable importance for texture engineering to enhance performance. However, their effects on thermoelectric and mechanical properties are still controversial and not clear yet. Moreover, there has been little documentation of mechanical properties related to micro-refrigeration applications. In this work, the above-mentioned methods are separately employed to control the macroscopic grain orientation for bulk n-type Bi 2 Te 3 samples. The HF method enabled the stabilization of both composition and carrier concentration, therefore yielding a higher quality factor to compare with that of LPHD samples, supported by DFT calculations. In addition to superior thermoelectric performance, the HF sample also exhibited robust mechanical properties due to the presence of nano-scale distortion and dense dislocation, which is the prerequisite for realizing ultra-precision machining. This work helps to pave the way for the utilization of n-type Bi 2 Te 3 for commercial micro-refrigeration applications., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

The hexagonal Bi 0.33 (Bi 6 S 9 )Br intermediate was incorporated to enhance the thermoelectric properties of Bi 2 S 3 by a facile synthesis process. As a result of the increase of carrier concentration caused by Br diffusion doping and the enhancement of phonon scattering caused by pores, point defects, and secondary phase interfaces, a maximum ZT value of 0.64 was achieved at 773 K in Bi 2 S 3 + 5% Bi 0.33 (Bi 6 S 9 )Br. This study provides a strategy for achieving Br doping in the Bi 2 S 3 system by adding the Bi 0.33 (Bi 6 S 9 )Br intermediate alloy, while the nanostructure was maintained in the matrix, which may be also suitable for other thermoelectric materials to obtain higher performance.

Discovering high-performance near-room-temperature thermoelectric materials is extremely imperative to widen the practical application in thermoelectric power generation and refrigeration. Here, ternary Ag 2 Se 1- x Te x ( x = 0.1, 0.2, 0.3, 0.4, and 0.5) materials are prepared via the wet-mechanical alloying and spark plasma sintering process to investigate their near-room-temperature thermoelectric properties. From density functional theory calculation and single-parabolic-band modeling study, we found that the reduced contribution of Se 4p orbitals to the total density of states decreases the carrier effective mass with increasing Te content, which should enhance the theoretically maximum zT . These calculation results are also verified by the experimental results. Meanwhile, complex microstructures including dislocations, nanograins, high-density boundaries, Te Se substitution, lattice distortions, and localized strain have been observed in ternary Ag 2 Se 1- x Te x . These complex microstructures strengthen phonon scattering and in turn lead to ultralow lattice thermal conductivity in the range of 0.21-0.31 W m -1 K -1 in ternary Ag 2 Se 1- x Te x at 300 K. Although the increased deformation potential suppresses the carrier mobility, benefiting from the engineered band structures and ultralow lattice thermal conductivity, a high zT of >1 can be potentially obtained in the ternary Ag 2 Se 1- x Te x with appropriate carrier concentration. This study indicates that ternary Ag 2 Se 1- x Te x is a promising candidate for near-room-temperature thermoelectric applications.

A Bi2Te3/Bi2S3@Bi nanocomposite with a network microstructure was successfully synthesized via a hydrothermal method and spark plasma sintering. This composite was constructed from Bi2Te3 nanoparticles and Bi2S3@Bi nanowires, and its network structure is beneficial for obtaining excellent thermoelectric performance. A ZT peak of 1.2 at 450 K was realized for the nanocomposite sample.